Add PPDProvider barebones implementation and associated cache skeleton.

chromeos/printing/ppd_cache.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROMEOS_PRINTING_PPD_CACHE_H_
+#define CHROMEOS_PRINTING_PPD_CACHE_H_
+
+#include <memory>
+#include <string>
+
+#include "base/files/file_path.h"
+#include "base/optional.h"
+#include "chromeos/chromeos_export.h"
+
+namespace chromeos {
+namespace printing {
+
+// PPDCache is manages a cache of locally-stored ppd files.  It stores

[skau, 2016/10/07 16:29:06]

typo (is)

[Carlson, 2016/10/14 19:28:56]

Done.

+// its cache in the directory pointed at by
+// PathService::Get(DIR_PRINTER_DRIVERS_CACHE).
+class CHROMEOS_EXPORT PPDCache {
+ public:
+  // Construction-time optional parameters.  These should all have defaults that
+  // are sane.
+  struct Options {
+    // Nothing here yet.  We may want to add ttl-style options
+    // here eventually.
+  };
+
+  static std::unique_ptr<PPDCache> Create();
+  static std::unique_ptr<PPDCache> Create(const Options& options);
+  virtual ~PPDCache() {}
+
+  // Look for a cached canonical PPD for the given manufacturer/model in the
+  // cache, and return it if it does exist.
+  //
+  // On success, the returned FilePath is guaranteed to remain valid until the
+  // next Store* call.
+  virtual base::Optional<base::FilePath> Find(
+      const std::string& manufacturer,
+      const std::string& model) const = 0;
+
+  // Look for a ppd previously cached with this key using AddLocal.  Return
+  // it if it does exist.
+  //
+  // On success, the returned FilePath is guaranteed to remain valid until the
+  // next Store* call.
+  virtual base::Optional<base::FilePath> FindLocal(
+      const std::string& key) const = 0;

[skau, 2016/10/07 16:29:06]

Would this be the appropriate place to document what we expect the key to be? 
Users of this function may not interact with Store*

[Carlson, 2016/10/14 19:28:56]

Obsolete

+
+  // Take the contents of a ppd file, store it to the cache, and return the
+  // path to the stored file.
+  //
+  // If this manufacturer-model tuple already exists, the new data will replace
+  // it.  Returns nothing on failure-to-store.  On failure, cache contents may
+  // be changed, but are guaranteed to remain coherent. It's reasonable to
+  // believe that a failure-to-store means something is very wrong in the system
+  // (out of disk or similar).
+  //
+  // On success, the returned FilePath is guaranteed to remain valid until the
+  // next Store* call.
+  virtual base::Optional<base::FilePath> Store(
+      const std::string& manufacturer,
+      const std::string& model,
+      const std::string& compressed_ppd_contents) = 0;
+
+  // Store a manually added ppd with the given key.  They key can be any
+  // arbitrary string of up to 256 characters.  Note that the keyspace for Local
+  // PPDs is completely disjoint from the keyspace for manufacturer/model stored
+  // PPDs -- one will never clobber the other due to a name collision.
+  //
+  // Returns nothing on failure-to-store.  On failure, cache contents may be
+  // changed, but are guaranteed to remain coherent.  It's reasonable to believe
+  // that a failure-to-store means something is very wrong in the system (out of
+  // disk or similar).
+  //
+  // On success, the returned FilePath is guaranteed to remain valid until the
+  // next Store* call.
+  virtual base::Optional<base::FilePath> StoreLocal(
+      const std::string& key,
+      const std::string& compressed_ppd_contents) = 0;
+};
+
+}  // namespace printing
+}  // namespace chromeos
+
+#endif  // CHROMEOS_PRINTING_PPD_CACHE_H_